This invention relates to rotary plug valves and, more particularly, to a molded-in-place valve having a seating ring between the rotary plug and the valve housing.
Rotary plug valves, especially those molded from plastic materials, have received wide acceptance in many types of liquid flow control applications. Among the numerous advantages of forming such valves of plastic materials are reduced fabrication costs and immunity of the valve to damage by many corrosive fluids. Examples of previously proposed plastic plug valves are described in U.S. Pat. No. 3,271,845 issued to Breher on Sept. 13, 1966, U.S. Pat. No. 3,807,692 issued to Usab et al on Apr. 30, 1974, U.S. Pat. No. 3,907,959 issued to Wise et al on Sept. 23, 1975, and U.S. Pat. No. 3,961,770 issued to Wrasman on June 8, 1976 and assigned to the assignee of this invention.
It has heretofore been proposed to fabricate rotary plug valves by a series of steps wherein a plastic plug, such as a ball, is initially molded and then is placed in the cavity of a mold which defines the valve housing. The housing is then molded-in-place around the plug to form a unitary plug-housing assembly. In either of its open and closed positions, the plug makes contact with an opposing sealing surface which may comprise a portion of the valve housing, or a seating ring disposed between the plug and the housing.
The valve described in the above-referenced Wrasman patent is of the type in which the plug engages a portion of the housing. While that valve performs satisfactorily in most systems, there are occasions in which the plug may tend to swell under the influence of certain fluids being conducted. As a result, the plug bears tightly against the sealing face and becomes difficult to turn. In those instances, it would be advantageous to utilize a seating ring disposed between the plug and housing and formed of low-friction material, to reduce turning torque. However, the use of seating rings presents certain problems, such as the danger of leakage between the seating ring and the housing, deformation or cold flow of the seating ring due to its inherent softness, and the possibility that turning of a swollen plug may still be difficult as the seating ring is compressed between the rigid housing and the plug.
It would be advantageous to provide a plastic rotary plug which avoids such problems while creating an effective fluid seal between the seating ring and the plug on the one hand and between the seating ring and the housing on the other hand.
It would also be desirable to enable a manual turning knob to be installed on the stem portion of the plug easily and quickly without the need for separate fasteners such as screws.
It is, therefore, an object of the present invention to provide a novel plug valve which minimizes problems of the sort discussed above.
It is another object of the invention to provide a novel rotary plastic plug valve which utilizes a seating ring to obtain an effective seal.
It is another object of the invention to provide a novel rotary plug valve which resists leakage and prevents excessive deformation of the seating ring.
It is still a further object of the invention to provide a novel rotary plug valve which is easily actuated despite swelling of the plug.
It is another object of the invention to provide a novel snap-on coupling for installing a manual turning handle on the stem of a rotary plug without requiring separate fasteners.